It has recently been brought to the attention of the authors of this article that a critical sensor error exists in the Exhalyser D device (Eco Medics AG, Duernten, Switzerland), pertaining to lack of compensation for crosstalk between the oxygen and carbon dioxide sensors. Updated software (Spiroware version 3.3.1) containing a correction for that error has since been distributed by the manufacturer.
Since the data in this study were collected using that device and reported using a previous software version (3.1.6), with potential implications on study results and interpretation, the authors have reanalysed the original data in the updated software. The updated tables and figures are shown below, and have been corrected in the published article. The supplementary material for this article has also been updated.
The authors confirm that the main messages of their article remain unaltered: that the indices of ventilation heterogeneity Scond and Sacin derived from free-breathing and controlled-breathing multiple-breath nitrogen washout protocols are not comparable, and that the differences in Sacin, in particular, are related to differences in the breathing pattern.
Participant characteristics, lung function and multiple-breath nitrogen washout (MBNW) parameters
Functional residual capacity measured by controlled breathing (FRCCB) and free breathing (FRCFB) protocols. a) There was strong correlation between the protocols (r=0.96, p<0.0001). b) Bland–Altman plot showing good agreement between the protocols (mean difference (95% limits of agreement) −0.009 (−0.592, 0.555) L, p=0.75).
Functional residual capacity measured by controlled breathing (FRCCB) and free breathing (FRCFB) protocols versus the gold-standard body plethysmography (FRCpleth). There was good correlation between FRC measured by both protocols and FRCpleth (r=0.86 and r=0.92, respectively, p<0.0001 for both). MBNW: multiple breath nitrogen washout.
Lung clearance index measured by controlled breathing (LCICB) and free breathing (LCIFB) protocols. a) There was strong correlation between the protocols (r=0.82, p<0.0001). b) Bland–Altman plot showing that free breathing produced a higher LCI compared to controlled breathing (mean difference (95% limits of agreement) 0.21 (−0.44, 0.87), p=0.003)). There was a trend towards proportional bias confirmed by linear regression (p=0.07).
Ventilation heterogeneity in conducting airways measured by controlled breathing (ScondCB) and free breathing (ScondFB) protocols. a) There was no significant correlation between the protocols (r=0.16, p=0.44). b) Bland–Altman plot showing high between-protocol variability (mean difference (95% limits of agreement) 0.0002 (−0.03, 0.03 L−1, p=0.94)). There was no evidence of proportional bias, regardless of outliers (p=0.83).
Ventilation heterogeneity in distal/intra-acinar airways measured by controlled breathing (SacinCB) and free breathing (SacinFB) protocols. a) There was relatively poor correlation between the protocols (r=0.33, p=0.11). b) Bland–Altman plot showing that free breathing produced higher Sacin compared to controlled breathing (mean difference (95% limits of agreement) 0.03 (−0.045, 0.103) L−1, p<0.0005)). There was also significant proportional bias confirmed by linear regression (p=0.002). The between-protocol difference in Sacin (SacinFB–SacinCB) was predicted by the between-protocol differences in c) tidal volume (VTFB−VTCB, regression p=0.004) and d) respiratory rate (RRFB−RRCB, regression p=0.009). One participant was excluded from Sacin analyses due to negative value in one trial.
Within- and between-session variability for the controlled and free breathing protocols
Acknowledgement
The authors wish to acknowledge the efforts of Sandra Rutting in the reanalysis of the data correcting for the sensor error for the preparation of this corrigendum as well as changes to the supplementary material.
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